The effect of deprivation of leftward movement on the organisation of the cat visual cortex is to be investigated. Cats will be raised inside a striped drum rotating to the right for one hour per day, and the rest of the time they will be in the dark. After several months of this treatment behavioral and physiological tests will be made on their visual system. A model for the directionally sensitive ganglion cells in the rabbit retina has been proposed, in which each point within the centre of the receptive field of the cell is inhibited from a cardioid shape area around it. This model can account for both directional sensitivity and size specificity with a single layer of lateral interconnections. It will be tested by recording from single cells in the retina. Some experiments on screening pigment migration have been done on the squid retina. One possible explanation of the results is that squid rhodopsin regenerates very slowly. This will be investigated.